The present invention relates generally to data storage systems. More particularly the present invention relates to a method of laser edge treating of sliders during manufacture.
Magnetic disc drives are information storage devices that use thin film magnetic media to store data. A typical disc drive includes one or more rotating rigid discs having concentric data tracks wherein data is read or written. The discs are mounted on a spindle motor that causes the discs to spin and the surfaces of the discs to pass under respective head gimbal assemblies. As the disc rotates, a transducer (or xe2x80x9cheadxe2x80x9d) is positioned by an actuator to magnetically read data from or write data to the various tracks on the disc. A head gimbal assembly can carry the transducer, which writes information to or reads information from a disc surface.
Typically, an actuator mechanism controlled by electronic circuitry moves the head gimbal amongst the tracks of the disc. The actuator mechanism can include a track accessing arm and a load beam for each head gimbal assembly. As a disc rotates at operating speeds, hydrodynamic pressure effects caused by air flow between the surface of the disc and an air bearing surface of the head cause the head to float above the disc. Once a predetermined rotational speed and head fly height (i.e., float height) is reached, reading and/or writing of data may commence. Maintaining proper fly height is essential to the accurate and reliable operation of the disc drive. The head gimbal assembly can include an air bearing slider and a gimbal. The gimbal can be positioned between the slider and a load beam thereby providing a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
Typically, a slider includes a slider body having an air bearing surface that faces the disc surface. As the disc rotates, air is forced under the slider along the air bearing surface in a direction approximately parallel to the tangential velocity of the disc. Friction on the air bearing surface causes the air pressure between the disc and the air bearing surface to increase. This air pressure creates a hydrodynamic lifting force that causes the slider to lift and fly above the disc surface. A pre-load force applied by the load beam is used to counteract and control the hydrodynamic lifting force. The point at which the pre-load force and the hydrodynamic lifting force reach equilibrium determines the flying height of the slider.
A transducer is typically mounted at or near the trailing edge of the slider. Flying height is viewed as one of the most critical parameters of contact and non-contact recording. As the average flying height of a slider decreases, the transducer achieves greater resolution between individual data bit locations on a disc. Consequently, it is desirable to have the transducers fly as close to the disc as possible. Flying height is preferably uniform regardless of variable flying conditions, such as tangential velocity variation from inside to outside tracks, lateral slider movement during seek operations and air bearing skew angles.
In certain applications, it is desirable to fabricate the slider such that the bearing surface has a positive curvature along the length and width of the slider. Length curvature is known as crown curvature. Width curvature is known as camber or cross curvature. The proper setting and control of length and width curvature improves flying height variability over varying conditions, improves wear on the slider and the disc surface, and improves takeoff performance by reducing stiction between the slider and the disc surface.
During slider fabrication, length or width curvature is resultant to lapping the bearing surface. Lapping is typically performed on a spherically-shaped lapping surface or on a flat lapping surface while rocking the slider body back and forth in the direction of a desired curvature. On the latter, the radius of the rocking rotation can determine the amount of curvature. Known lapping processes can be difficult to control resulting in varying amounts of curvature. In addition, in typical slider processing compressive machining stresses are left on the edges of the thin film head slider following a dicing operation. Since the air bearing surface curvature has initially been determined at the bar level prior to dicing, these slider edge stresses alter the flatness and leave unwanted slider ridges (or abrupt increases in cross curve near the rail edges).
Various methods of providing tensile stress to the back surface of a slider body have been used to control the curvature of the body. U.S. Pat. No. 5,982,583 discloses melting and then cooling the back surface of a slider to add tensile stress and, thereby inducing curvature of the bearing surface. A laser beam is scanned across the back surface of a slider body to induce this melt condition. Other techniques include altering stresses from the back of a slider through the use of a micro sandblast tool or laser to pattern the back of the slider. Patterns can be chosen to modify camber and/or crown curvature. Camber and crown modification can take place while the sliders are still in a row, or after separation into individual sliders.
However, decreasing fly heights and continued miniaturization requires still more control over slider curvature. More efficient and controllable methods of affecting air bearing surface curvatures are desirable.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.
The present invention provides a method for Laser Edge Treating (LET) a slider during processing, and a slider with laser edge treatment, wherein the laser treatment is used to modify the curvature of a slider edge. The laser can also be used to alter ridges along the slider edge and to make positive and negative adjustments to the crown and cross curve. LET is effective after slider dismount to precondition the crown and cross curve prior to slider level crown adjustment. The LET can also be applied to a slider edge at the bar assembly level following the dicing operation as a blind batch treatment.
A ridge formed along the dicing edge of a disc head slider can be controlled by applying heat to slider material along a path that follows a dicing path which is used to fabricate the slider. The heat must be sufficient to alter stresses created by the dicing process. As a result of the heating, a reduction, or elimination of an alteration of the curvature along the air bearing surface occurs, which may result in an alteration of the dicing edge ridge. The heat can be applied with a laser or other concentrated heat source.
In one embodiment, the laser is applied to a slider edge. This can be accomplished, for example, by directing the laser into a dicing slit of a wafer bar assembly of slider material.
In addition, the present invention can be utilized to control crown, cross curve, and twist on the slider. Control can be accomplished by varying the pattern used to apply the heat to the slider. Patterns can include, for example, beginning close to an air bearing surface of the slider material and proceeding towards a back surface of the slider material. Another pattern can begin close to a backside surface of the slider material and proceed towards an air bearing surface of the slider material. Another pattern can begin within a middle portion of the slider edge and alternately proceeding outwards towards an air bearing surface and a back surface of the slider material. Still another pattern can be applied to only a portion of the dicing edge, either near the leading edge, or near the trailing edge of the slider to control the twist curvature.
In another aspect of the invention, a disc head slider can include an air bearing surface and a back surface, which is opposite the air bearing surface. A plurality of dicing edges can join the air bearing surface and the back surface. Along a dicing edge a ridge can be reduced or eliminated by thermal relaxation of compressive stress, and by adding tensile stress.